You can absolutely use 2 x Sequence 8’s to make a 16 Step Sequence, although you will have to use a Clock Divider and a Sequential Switch in your system in order to do pull this off.

Run one Sequence 8’s Clock Out to the second Sequence 8’s Clock In, then take second Sequence 8 Clock Out and run into a Clock Divider with an EVEN division. Take the Divided by 16 Clock Out and run into the Clock / Trigger input of a Sequential Switch. Run one CV out from the 1st Sequence 8 into Channel 1 on the Sequential Switch, and run one CV out from the 2nd Sequence 8 into Channel 2 on the Sequential Switch. Now the Sequential switch will switch between the 2 channels evenly, and you can run the output from the Sequential Switch into a 1v/Oct input on your VCO and you’ll have a 16-step sequence. Bam!